DC-DC converter with reduced ripple

ABSTRACT

A DC/DC converter is provided which can be produce easily and inexpensively with an alternating current component with which a superimposed direct current is reduced in an output voltage (ripple). A C+DC/DC converter includes an input and output, a series arm which is arranged between the input and the output and in which at least one first inductor and first capacitor are arranged, and a capacitor arranged in a first shunt arm at the output. A second shunt arm arranged parallel to the first shunt arm is equipped with a first switch and a second switch arranged in series and a second inductor such that the first connection of the inductor is connected to a point between the first inductor and the first capacitor and the second connection of the inductor is connected to a point between the first and the second switch.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/063,320, filed on Jun. 18, 2018, which is the U.S. National Stage ofInternational Application No. PCT/DE2016/100608, filed Dec. 21, 2016,which designated the United States and has been published asInternational Publication No. WO 2017/108033 A1 and which claims thepriority of German Patent Application, Serial No. 10 2015 122 567.0,filed Dec. 22, 2015, pursuant to 35 U.S.C. 119(a)-(d) the description ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a DC/DC converter having an input and anoutput, a longitudinal arm arranged between the input and the output, inwhich at least a first inductor and a first capacitor are arranged, anda capacitor arranged in a first shunt arm at the output, and anothershunt arm with different arrangements of a second inductor and twoswitches.

In many areas of technology it is necessary to convert an available DCvoltage to operate connected loads. Such a conversion of an availableso-called supply input voltage Ue can be performed, for example, with aDC/DC converter, wherein the DC/DC converter can generate for theconnected loads an output voltage Ua which is smaller or larger than theinput voltage Ue.

Such DC converters find application, for example, in machines orindustrial plants, in a variety of electronic devices and in vehiclemanufacturing. For example, such DC converters are customary inso-called switching power supplies, which are often used in computers,notebooks, mobile phones, hi-fi devices and small motors.

The advantages of such converters are improved efficiency and reducedheat generation.

To convert the electrical energy, so-called clocked converters aretypically used as DC/DC converters, which are controlled with a controlsignal, which determines the clock signal for switching the singleswitch arranged in the converter. Customarily, one or more passiveelectrical storage devices, such as capacitors and/or inductors, arearranged in such converters. The operating principle for converting aninput voltage into an output voltage is a controlled cyclic charging anddischarging of the passive electrical storage devices.

For example, active, electrical semiconductor switches such as a BJT(Bipolar Junction Transistor), a MOSFET (Metal-Oxide-SemiconductorField-Effect-Transistor) or an IGBT (Insulated Gate Bipolar Transistor)are used instead of a switch required in the DC/DC converter.

The result at the input and/or output of power controller is atriangular current curve or voltage curve due to the cyclic charging anddischarging of the passive electrical storage devices, such ascapacitors and/or inductors. This effect is also referred to as rippleand represents an alternating current of an arbitrary frequency andwaveform superimposed on a direct current. Also used is the concept of apulsating direct current.

These high-frequency ripples generate harmonics which cause disturbancesin other connected electronic components. To limit these interferingelectromagnetic fields, attempts are generally made to attenuate theripple by using larger or additionally employed components. Suchapproaches can be found in “A ‘Zero’ Ripple Technique Applicable To AnyDC Converter” David C. Hamill, Surrey Space Center, University ofSurrey, Guildford, UK, d.hamill@surrey.ac.uk and in Ripple SteeringAC-DC Converters to Minimize Input Filter, Eric CHOU, Frank CHEN,Claudio Adragna, Bruce LU.

Furthermore, ideas have been proposed to reduce ripple by additionalactive sources, as disclosed in Techniques for Input Ripple CurrentCancellation: Classification and Implementation, N. K. Poon, J. C. P.Liu, C. K. Tse and M. H. Pong. Alternatively, modifications to minimizedisturbances with coupled inductors are also known from AN3180,Application Note, A 200 W ripple-free input current PFC pre-regulatorwith the L6563S, (c) 2010 STMicroelectronics.

SUMMARY OF THE INVENTION

The object of the invention is to provide a DC/DC converter, which issimple and inexpensive to produce and whose alternating currentcomponent which is superimposed on a direct current in an output voltage(ripple) is reduced.

The object is achieved by a device having the features according toclaim 1, 3, 5 or 7 of the independent claims. Further developments arerecited in the dependent claims 2, 4, 6 and 8.

It is contemplated to implement the DC/DC converter in such a way thatat least an inductor and a capacitor are arranged in a longitudinal arm.An additional capacitor is arranged in an output-side shunt arm. In afirst variant, two switches are arranged in a parallel circuit connectedin parallel with this output-side shunt arm, wherein a center tapbetween these two switches is connected with a first terminal of afurther inductor. The second terminal of this inductor is connected to apoint between the inductor arranged in the longitudinal arm and thecapacitor.

In an alternative embodiment of the DC/DC converter, it is provided toarrange an inductor and a switch in the further shunt arm instead of thetwo switches. In this series connection, the position of the twocomponents may also be interchanged. The point located between the twocomponents is connected to a terminal of a first switch whose secondterminal is connected to a point between the inductor and the capacitorarranged in the longitudinal arm.

Advantageously, active semiconductor switches may be used for theswitches in the DC/DC converter.

These active semiconductor switches may be, for example, a BJT, a MOSFETor an IGBT. However, possible embodiments are not limited to theselisted semiconductor switches.

BRIEF DESCRIPTION OF THE DRAWING

Further details, features and advantages of embodiments of the inventionwill become apparent from the following description of exemplaryembodiments with reference to the appended drawings where:

FIG. 1: is a prior art DC/DC converter (SEPIC-Converter),

FIG. 2 is a first implementation of the DC/DC converter according to theinvention,

FIG. 3: is a second implementation of the DC/DC converter according tothe invention,

FIG. 4 is a third implementation of the DC/DC converter according to theinvention,

FIG. 5 is an application of the DC/DC converter according to theinvention in an AC bridge, and

FIG. 6 is a graphical representation of detected ripple in comparisonbetween the prior art and the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a prior art DC/DC converter 1. The illustrated DC/DCconverter 1 is a so-called SEPIC-Converter (SEPIC—Single Ended PrimaryInductor Converter), which was selected as a representative example ofthe group of non-galvanically separating converters which areconstructed with passive 4 storage devices, for example two capacitorsand two inductors. The characteristic of this DC/DC converter enablesoperation in such a way that the output voltage can be smaller orgreater than the input voltage.

The DC/DC converter 1 has an input 2 to which an input voltage Ue can beapplied, and an output 3 at which an output voltage Ua is supplied thathas been converted by the DC/DC converter 1. The DC/DC converter 1 maysupply an output voltage Ua which may be larger or smaller than theinput voltage Ue.

The DC/DC converter 1 has in a longitudinal arm a first inductor 4, afirst capacitor 5 and a diode 6. In an output-side shunt arm, a secondcapacitor 8 is arranged in parallel with a load resistor connected tothe output 3, which is not shown in FIG. 2. In a further shunt arm, asecond inductor 7 is arranged between the first capacitor 5 and thediode 6. A first switch 9 is also arranged in a third shunt arm betweenthe first inductor 4 and the first capacitor 5.

When the switch 9 in the DC/DC converter 1 shown in FIG. 1 is closed,the input voltage is present at the first inductor 4. Simultaneously, avoltage having a value corresponding of the input voltage at the input 2is present at the first capacitor 5. The current flowing through thefirst and second inductor 4 and 7 increases, with energy being stored inthe inductors 4 and 7.

At this time, the second capacitor 8 arranged at the output sidesupplies the output current for a connected load or a consumer, sincethe diode 6 is blocking. When the switch 9 is opened, the polarity ofthe voltages at the first and second inductors 4 and 7 is reversed. Thediode 6 turns on and supplies the stored energy to the second capacitor8 and thus also to the connected load.

FIG. 2 shows a first implementation of the DC/DC converter 1 accordingto the invention. The DC/DC converter 1 has in its longitudinal arm,i.e. between its input 2 and its output 3, at least a first inductor 4and a first capacitor 5. A second capacitor 8, which is connected inparallel to an unillustrated load at the output 3, is arranged in anoutput-side shunt arm.

A first switch 9 and a second switch 10 connected in series are alsoarranged parallel to the output 3 and the second capacitor 8. A secondinductor 7 is disposed between the first inductor 4 and the firstcapacitor 5 and a terminal disposed between the series-connectedswitches 9 and 10.

Preferably, the switches 9 and 10 are implemented as activesemiconductor switches. For example, BJT (Bipolar Junction Transistor),MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), IGBT(Insulated-Gate Bipolar Transistor) or others switches may be used.

It is contemplated to control the switches with a control signalgenerated by a central controller 12 shown in FIG. 2. The centralcontroller 12 provides the control signals for the mechanical orelectronic switches 9 and 10 such that the switches 9 and 10 areactivated alternately. Thus, the switch 9 is closed when the switch 10is opened and vice versa.

In the circuit arrangement according to the invention shown in FIG. 2,the direction of the current flow is dependent on a selected duty cycleof the control signals of the switches 9 and 10 as well as on thevoltages Ue and Ua present at the input 2 and at the output 3.

The switches 9 and 10 can be controlled using the method of state-spaceaveraging and a special form of zero-voltage switching, wherein theoscillating circuit is arranged parallel to the switch and is activelyexcited to oscillate by an additional switching pulse.

The DC/DC converter 1 in FIG. 2 is able to generate from an inputvoltage Ue applied to the input 2 a larger output voltage Ua at theoutput 3. In such a DC/DC converter 1, ripple is reduced in accordancewith the invention, i.e. the pulsating direct current at the input 2 issmaller. The input can be interchanged with the output, thus reversingthe operation. When an input voltage Ue is applied to the output 3 andthe DC/DC converter 1 is controlled accordingly, an output voltage Ua issupplied at the input 2 which is, for example, less than Ue.

In the event that the operation of the DC/DC converter is reversed, thereduced ripple is no longer present at the input side of the converter,but rather at the output side.

FIG. 3 shows a second Implementation of the DC/DC converter 1 accordingto the invention. The DC/DC converter 1 has in its longitudinal arm,between its input 2 and its output 3, at least a first inductor 4 and afirst capacitor 5. A second capacitor 8, which is connected in parallelto an unillustrated load at the output 3, is arranged in an output-sideshunt arm.

Moreover, a second inductor 7 and a second switch 10 connected in seriesare arranged in parallel with the output 3 and the second capacitor 8. Afirst switch 9 is arranged between the first inductor 4 and the firstcapacitor 5 and a terminal disposed between the second inductor 7 andthe first switch 9.

FIG. 4 shows a third implementation of the DC/DC converter 1 accordingto the invention. The DC/DC converter 1 has in its longitudinal armbetween its input 2 and its output 3 at least a first inductor 4 and afirst capacitor 5. A second capacitor 8, which is connected in parallelto an unillustrated load at the output 3, is arranged in an output-sideshunt arm.

Likewise, a second switch 10 and a second inductor 7 connected in seriesare arranged parallel to the output 3 and the second capacitor 8. Asecond switch 9 is connected between the first inductor 4 and the firstcapacitor 5 and a terminal disposed between the series-connectedelements switch 10 and second inductor 7.

In the DC/DC converter 1 shown in FIG. 4, the polarity of the voltage atthe output 3 is inverted.

The switches 9 and 10 can be controlled by the method of state-spaceaveraging as well as a special form of zero-voltage switching, whereinthe oscillating circuit is parallel to the switch and is activelyexcited to oscillate by an additional switching pulse.

In the event that an active semiconductor switch, such as an IGBT or aMOSFET, is used for the switches 9 and/or 10, these switches 9 and/or 10form a diode in a state in which the switch 9 and/or 10 is/are notactivated. This diode allows a directed current flow. In the case whereone or both switches 9 and/or 10 is/are activated, the semiconductorswitches have a very low transfer resistance and enable current flow inany direction.

FIG. 5 shows an application of the DC/DC converter 1 in an AC bridge. Inorder to generate, for example, a sinusoidal AC voltage required for aload, such as a motor, two DC/DC converters 1 are used. A voltage sourceis connected on the input side to the inputs of both DC/DC converters 1.The DC/DC converter 1 shown in the upper part of FIG. 5 generates apositive half-wave in response to corresponding control signals for theswitches 9 and 10 in the DC/DC converters 1. This is shown in FIG. 5 ina small diagram with a current-time profile of the current I1. Thenegative half-wave is generated by the lower DC/DC converter 1. Thecorresponding profile of the current I2 is also shown in a smalldiagram.

It has been demonstrated, when comparing a DC/DC converter 1 accordingto the invention of FIG. 2 with a prior art SEPiC-Converter that thedisturbing ripple could be greatly reduced. As shown in part in FIG. 6,comparative measurements have shown that the SEPIC-Converter, shown inthe upper part of the current-time profile, exhibits ripple currents inthe range of about 4 A, whereas the converter according to the inventionshown in the lower part of the current-time profile, had a ripplecurrent in the range of about 4 mA. Thus, the ripple could be greatlyminimized by virtue of the invention.

The invention can be used in many areas for the conversion of electricalenergy, such as in the

Unidirectional or bidirectional DC/DC conversion,

Extension of DC version to an AC bridge,

impedance spectroscopy of energy sources (low ripple),

Control of electric motors or

Battery charging in battery management systems.

An exemplary application of the invention in impedance spectroscopy willbe described below.

The characteristic impedance of an electrochemical energy source, suchas an accumulator or a fuel cell, provides information about theinternal states of the source, in order to measure the impedance, thesource is either supplied with a targeted disturbing current and thevoltage response is measured, or a disturbance voltage is superposed onthe source, and the reaction of the current is detected. In both cases,the ripple current or the ripple voltage is superposed on this targetedinterference signal. The effect of the ripple current can besignificantly reduced with the illustrated invention, thus allowing asignificantly improved impedance measurement, which is hardly affectedby disturbances.

The DC/DC converter according to the invention advantageously reducesripple without the need to resort to additional, larger or differentcomponents in the DC/DC converter circuit. Another advantage is that thecomponents used in the DC/DC converter have no specific dimensioningrequirements.

What is claimed is:
 1. A DC/DC converter comprising: an input and anoutput, a longitudinal arm arranged between the input and the output andhaving at least a first inductor and a first capacitor, a first shuntarm connected across the output, a second shunt arm having a firstactive semiconductor switch and a second active semiconductor switch andforming a serial circuit having two end connection points which areconnected directly to respective terminals of the output, and a centerconnection point, wherein a terminal of the first active semiconductorswitch facing away from the second active semiconductor switch isconnected directly to a terminal of the first capacitor of thelongitudinal arm and is connected directly to the output, and a secondinductor having a first terminal connected to a point between the firstinductor and the first capacitor and a second terminal connected to thecenter connection point, and a controller providing control signals tothe first and second active semiconductor switches such that the firstand second active semiconductor switches are activated alternately,closing the first active semiconductor switch is when the second activesemiconductor switch is opened and vice versa, wherein the input and theoutput are interchangeable, thereby allowing bi-directional operation ofthe DC-to-DC converter.
 2. The DC-to-DC converter according to claim 1,wherein the first and second active semiconductor switches are a BJT(Bipolar Junction Transistor), a MOSFET (Metal-Oxide-SemiconductorField-Effect-Transistor) or an IGBT (Insulated Gate Bipolar Transistor).3. A DC/DC converter comprising: an input having an applied inputvoltage with a first polarity, an output generating an output voltagewith a second polarity, a longitudinal arm arranged between the inputand the output and having a first inductor and a first capacitor, afirst shunt arm connected across the output, a second shunt armconnected parallel to the first shunt arm and having a second activesemiconductor switch and a second inductor connected in series, whereina terminal of the second active semiconductor switch facing away fromthe second inductor is connected directly to the output, and a firstactive semiconductor switch having a first terminal connected to a pointbetween the second active semiconductor switch and the second inductorand a second terminal connected to a point between the first inductorand the first capacitor, wherein the second polarity is inverted withrespect to the first polarity.
 4. The DC-to-DC converter according toclaim 3, wherein the first and second active semiconductor switches area BJT (Bipolar Junction Transistor), a MOSFET (Metal-Oxide-SemiconductorField-Effect-Transistor) or an IGBT (Insulated Gate Bipolar Transistor).5. A method for operating a DC-to-DC converter, comprising: connecting afirst inductor and a first capacitor in series between an input and anoutput of the DC-to-DC converter, connecting a first shunt arm acrossthe output, forming a second shunt arm of a serial circuit consisting ofa first active semiconductor switch and a second active semiconductorswitch, the serial circuit having two end connection points, which areconnected directly to respective terminals of the output, and a centerconnection point, wherein a terminal of the first active semiconductorswitch facing away from the second active semiconductor switch isconnected directly to a terminal of the first capacitor and is connecteddirectly to the output, connecting a first terminal of a second inductorto a point between the first inductor and the first capacitor andconnecting a second terminal of the second inductor to the centerconnection point, and alternately activating the first and second activesemiconductor switches such that the first active semiconductor switchis closed when the second active semiconductor switch is opened and viceversa, further comprising interchanging the input and the output andperforming bi-directional operation of the DC-to-DC converter.
 6. Themethod of claim 5, wherein the first and second active semiconductorswitches are a BJT (Bipolar Junction Transistor), a MOSFET(Metal-Oxide-Semiconductor Field-Effect-Transistor) or an IGBT(Insulated Gate Bipolar Transistor).
 7. A method for operating aDC-to-DC converter, comprising connecting a first inductor and a firstcapacitor in series between an input and an output of the DC-to-DCconverter, connecting a first shunt arm across an output, forming asecond shunt arm of a serial circuit consisting of a second inductor anda second active semiconductor switch, connecting a terminal of thesecond active semiconductor switch facing away from the second inductordirectly to the output, connecting a first terminal of a first activesemiconductor switch to a point between the second active semiconductorswitch and the second inductor, connecting a second terminal of thefirst active semiconductor switch to a point between the first inductorand the first capacitor, applying to the input an input voltage with afirst polarity, and generating at the output of the De-to-DC converteran output voltage with a second polarity that is inverted with respectto the first polarity.
 8. The method of claim 7, wherein the first andsecond active semiconductor switches are a BJT (Bipolar JunctionTransistor), a MOSFET (Metal-Oxide-SemiconductorField-Effect-Transistor) or an IGBT (Insulated Gate Bipolar Transistor).